1. Field of the Invention
This invention relates to an engine ignition system.
2. Prior Art
Electronic engine control systems are known which include spark timing control as one of the controlled parameters. Spark timing is determined as a function of engine rpm and engine load by a software program in a microcontroller. For example, timing reference for spark timing can be obtained from a profile ignition pickup (PIP) or crankshaft position sensor. An ignition module is coupled to the engine control computer and receives timing information from the controller. The ignition module provides the power necessary to drive the ignition coil. Because of the complex nature of the system, failure to produce a spark can be due to failure of any of the components, such as, for example, the crankshaft (PIP) sensor, the processor control module or the ignition control module. Several methods for monitoring the primary ignition system operation and detecting, storing, and, in some cases, isolating faults would be desirable. These are some of the problems this invention overcomes.
U.S. Pat. No. 3,970,872 issued to Kuhn et al teaches a circuit for analyzing ignition voltage waveforms of an internal combustion engine. The circuit includes a monostable multivibrator which is triggered in response to the detection of a spark pulse to generate a blanking voltage. A trigger blanking voltage is useful in analyzing ignition voltage waveforms. After initial triggering occurs, it may be desirable to blank out further triggering signals which might occur during the course of ignition and which could reinitiate a measuring or analysis cycle. Connected to the output of the monostable multivibrator is a capacitor charging circuit with an electrode of the capacitor therein coupled back to the RC circuit which determines the duration of the unstable state of the flip flop.
U.S. Pat. No. 3,965,677 issued to Goto et al and U.S. Pat. No. 3,908,366 issued to Masaki teach misfire detecting apparatuses for internal combustion engines. The patent to Goto et al detects misfiring by monitoring exhaust gas pressure and the patent to Masaki detects misfiring by using a gas current pulse generator in the exhaust manifold of the engine.
U.S. Pat. No. 4,040,294 issued to Matsuda et al teaches an apparatus for detecting misfire in an internal combustion engine in which misfire is detected by monitoring the change in the tone of the exhaust sound. These three patents involve detection of a misfire in the cylinder, whether or not it is due to a missing spark. Accordingly, detection of such a fault could not be attributed to a missing spark. For example, poor air fuel ratio could also be a cause. It would be desirable to have an ignition diagnostic monitor circuit to detect the loss of an ignition coil primary coil pulse and to use the microcomputer of an engine control system to detect and store the fault in a keep-alive memory for later retrieval by a service technician. Additonally, it would be desirable to isolate and identify the source of the fault.